Transformation of hollow-core screw dislocations: transitional configuration of superscrew dislocations

Hollow-core screw dislocations along [0001] in hexagonal silicon carbide single crystals, i.e. micropipes, are known to heal or close during annealing or epitaxial growth procedures. Although the healing and closing are understood to be caused by the dissociation of hollow-core superscrew dislocations into multiple closed-core elementary screw dislocations with Burgers vector of 1c, the transformation mechanism, especially in terms of elastic energy, is unclear. Here, we propose a unique transitional configuration of the super-screw dislocations based on theoretical considerations to well explain the transformation mechanism, which consists of a 1c-screw-dislocation cluster and dense basal-plane partial dislocation loops. An elastic energy calculation revealed that the activation energy for the loop creation based on the proposed model well explains experimentally derived tendencies of the healing process. Furthermore, we confirmed that the total elastic energy of a healed micropipe is lower than those of 1c-screw-dislocation clusters without dislocation loops and hollow-core micropipes.